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Thin Solid Films 520 (2011) 16681678

Contents lists available at ScienceDirect

Thin Soli

w.ecan signicantly increase the risk of lung cancer. As a result, Cr(VI)-based coatings are being phased out but nding a suitablereplacement has proved challenging.

Extensive research has been invested for designing alternativeeco-friendly technologies such as anodization [1], solgel treatment[26], pigmented coatings [7], conductive pigments/polymers, pig-ment-based cathodic protection [8,9], green chemical conversioncoatings [1018], and aluminum nitride thin lms [1925].

organic compounds. When used with a non-chromate conversioncoating, an environmentally acceptable anti-corrosion coating systemwould be obtained.

Conversion coatings are aqueous chemical surface treatmentsthat provide metallic surfaces with increased corrosion resistanceand enhanced paint adhesion. Work done at MPI, together withother previous research work [17,18,2629]; have identiedvanadium oxide-based conversion coatings (VCC) as potentiallyThis paper addresses part of our researchInstitute (MPI), focuses on a two-layer coatnon-chromate conversion coating layer and a

Corresponding author. Max Planck Institute ofMhlenberg 1, 14476 Potsdam, Germany. Tel.: +202 25

E-mail address: asalam85@yahoo.com (A.S. Hamdy)

0040-6090/$ see front matter 2011 Elsevier B.V. Adoi:10.1016/j.tsf.2011.05.080romate primer over thee primer (see Fig. 1).human carcinogen that

(such as epoxy, uoropolymer,etc.) is an attractive alternative tothe existing systems, as it would reduce the complexity of the coatingsystem into two layers while at the same time reducing volatileconversion coating, and a topcoat over thHowever, chromium has been identied as ahexavalent chromium (Cr(VI)) conve1. Introduction

The typical aluminum surface is cooxide lm. However, this thin layer iscorrosion agents and does not yieldlayers of the coating. Moreover, thelements such as copper in AA2024 allcorrosion attack by forming galvanic c

Coating systems used for militar

with the metallic substrate, a strontiy a 37 nm thick naturalcient to protect againstadhesion to subsequentence of some alloyingicularly increases pitting.raft typically employ aoating in direct contact

Previous efforts to replace the chromate-based coatings inparticular chromate primers with more benign materials have hadsome success. For example, a chromate-free primer developed forseveral magnesium and aluminum alloys and composites [118].However, non-chromate primers based on cerium salts, for example,are relatively expensive and a long treatment time is needed.

Introducing environmentally benign such as vanadia basedconversion coatings prior to a commercially available top coatingsactivities at Max Plancking system, including acommercially available,

viable corrosionsion coatings onThe VCCs showaluminum allocommercial airc

The coatingssodium vanadatprocessing techn

Colloids and Interfaces, Am010640; fax: +202 25010639..

ll rights reserved.h-strength aluminum alloys (Fig. 1).Intelligent self-healing corrosion resistan

Abdel Salam Hamdy a,b,, I. Doench b, H. Mhwald b

a Central Metallurgical Research and Development Institute, CMRDI, P.O. Box: 87, Helwan,b Max Planck Institute of Colloids and Interfaces, Am Mhlenberg 1, 14476 Potsdam, Germ

a b s t r a c ta r t i c l e i n f o

Available online 14 June 2011

Keywords:Chemical conversion coatingsVanadiaEISAA2024Surface treatmentSelf-healingProtective lmsCyclic voltammetryMarine corrosion

This paper is a continuationfor aluminum and magnesipaper, a simple vanadia baseof high strength AA2024 acorrosion behavior was inveevaluate the electrochemicasalt per liter showed the beThe optimum conditions texamination of the samples

j ourna l homepage: wwanadia coating for AA2024

ro, Egypt

our investigation into the designing of chromate-free anti-corrosion coatingsbased materials for marine, automotive and aerospace applications. In thishemical conversion coating was applied for improving the corrosion resistance. The effect of vanadia solution concentrations (10, 30 and 50 g/l) on theated. EIS, linear polarization and cyclic voltammetry techniques were used tohavior in 3.5% NaCl. Vanadia coatings prepared by dissolving 10 g of vanadatecalized corrosion resistance as measured by EIS and polarization techniques.btain corrosion protective coatings for AA2024 were determined. Surfaces investigated using AFM, SEM-EDS and macroscopic images.

2011 Elsevier B.V. All rights reserved.

d Films

l sev ie r.com/ locate / ts finhibitors and replacements for chromate conver-magnesium and aluminum alloys and composites.promise for corrosion protection to high-strengthys, such as the 2024-T3 used in military andraft.are deposited from aqueous solutions containinge using a very simple spontaneous free immersionology that is very similar to that currently used for

the toxic chromate system. A thin layer of vanadium oxide conversioncoatings is deposited on the aluminum alloy surface by a chemicallydriven deposition process. Typically, uniformly distributed compactcoatings of thickness about 1 to 1.2 m were deposited. Depositionsare achieved in 10 min and use commercially available chemical,materials and equipment, making the overall process compatible withindustrial operations such as those employed by current automotive

and thus adhesion. For thin lms formed from the gas phase, theadhesion is generally promoted by including plasma pre-sputtering,which removes the surface oxide, before forming the new layer. Incase of solid-phase-formed lms, surface properties such asroughness are important and, therefore, the substrate is commonlypolished before the next layer is formed. In case of liquid-phase lmformation, as concerned in this project, chemical surface modiersusing alkaline etching in 1 M NaOH solution at 60 C followed byacidic pickling in 20% HNO3 at room temperature are applied priorto the new vanadia lm being formed.

Coatings that result from these processes are composed mostlyof vanadium oxide phases. The operating parameters and condi-tions used to deposit the coating signicantly inuence the qualityand performance of the deposited lms. Three critical steps in

Fig. 1. A schematic representation (not to scale) showing (a) the three layers of a conventional toxic chromate-containing corrosion protection system and (b) the two layervanadium oxide coating technology in the system being developed by the MPI team.

Table 1Chemical composition (wt.%) of AA2024 T3.

Element Cu Si Fe Mg Mn Al

wt.% 4.46 0.18 0.28 1.35 0.64 Balance

1669A.S. Hamdy et al. / Thin Solid Films 520 (2011) 16681678and aircraft manufacturers.The adhesion performance can be improved simply by cleaning

the substrate surface prior to vanadia coatings, but these solventsusually remove only oils and greases, leaving more tenaciousmaterials such as surface oxides, which may prevent inter-diffusion

aUncoated Surface defects

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Fig. 2. SEM-EDS for the blank samples before (a) and after (b) corrosion in 3.5% NaCl solutioproducing the vanadium oxide conversion coatings are surfacepreparation, vanadia coating concentration and pH, and post-deposition treatment using hot air drying. This paper will focuson investigating the effect of vanadia coating concentration on thecorrosion protection performance of AA2024 T3.

bUncoated

Pitting corrosion ounts

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n for one week. The images focus into the surface defects and localized corrosion zones.

Studies to improve and optimize these critical steps wereconducted thoroughly during this project for some magnesium andaluminum alloys. The corrosion behavior was studied in 3.5% NaClsolution by means of EIS and cyclic voltammetry techniques. Surfaceexamination was performed by AFM, SEM-EDS and visual inspection.

2. Experimental

2.1. Materials and surface preparation

Specimens of AA2024 alloy in the form 3060 mm taken fromsheet of 3 mm thick were abraded to 800 # nish with SiC grit papers,degreased in acetone, washed with distilled water, and dried in dryair. The chemical composition (wt.%) is given in Table 1.

2.2. Solutions and surface treatment

Solutions used in this work were prepared using sodium vanadatesalt with different vanadia solution concentrations. The AA2024substrates were treated by simple free immersion in vanadia solutionsunder the following conditions:

1. As polished (as a blank) without vanadia coatings2. Treatment in 10 g/l NaVO3 solutions for 10 min3. Treatment in 30 g/l NaVO3 solutions for 10 min4. Treatment in 50 g/l NaVO3 solutions for 10 min

After coatings, the samples of each group were washed withnano-pure water and dried with hot air. A comparison will be made

a

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Nucleation of vanadia over a pitting zone

(Self-healing)10 g/l

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Fig. 3. SEM-EDS for the vanadia coated (10 g/l) samples before (a) and after (b) one we

corroded zones and the self-healing tendency due to vanadia.Flower like morphology

)

n 3.5% NaCl solution. The images focus into the nucleation of vanadium oxide over the

between the corrosion resistances during seven days of immersionin 3.5% NaCl solution.

2.3. Testing

2.3.1. Electrochemical impedance spectroscopy (EIS)EIS technique was used to evaluate the electrochemical behavior

of the uncoated (as-polished) and coated AA2024 samples in 3.5%NaCl solution open to air and at room temperature for up to sevendays. A three-electrode set-up was used with impedance spectrabeing recorded at the corrosion potential Ecorr. A saturated calomelelectrode (SCE) was used as the reference electrode. It was coupledcapacitively to a Platinum wire to reduce the phase shift at highfrequencies. EIS was performed between 0.01 Hz and 65 kHzfrequency range using a frequency response analyzer (Electro-

chemical analyzer instrument: CompactStat Ivium Soft 1.805Release IVIUM Technologies Netherlands). The amplitude of thesinusoidal voltage signal was 10 mV. The exposed surface area was4 cm2. All curves were normalized to 1 cm2.

2.3.2. Cyclic voltammetry measurementsCyclic voltammetry measurements of the samples previously

immersed for seven days in 3.5% NaCl solution were made at a scanrate of 0.07 mV/s using CompactStat Ivium Soft 1.805 Release IVIUMTechnologies Netherlands. The potential was recorded starting froma cathodic potential (100 mV) and allowed to sweep to anodicpotential direction till a sudden shift in the current to the activedirection was observed. At that point the sample was enforced tosweep again in the cathodic direction. The exposed surface area was4 cm2. All curves were normalized to 1 cm2.

a

b30 g/l 30 g/l

30 g/l

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1671A.S. Hamdy et al. / Thin Solid Films 520 (2011) 16681678Counts

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Fig. 4. SEM-EDS for the vanadia coated (30 g/l) samples before (a) and after (b) one w

vanadia concentration.Energy (keV)4 6

in 3.5% NaCl solution. The images focus into the healing behavior with increasing the

2.3.3. Surface characterizationSEM and EDS were used to examine the surface morphology of the

coated samples before and after the immersion in 3.5% NaCl solution.SEM images of the samples that immersed in 3.5% NaCl for seven days,washed with deionized water and then dried were obtained using aGemini LEO 1550, 3 kV operating voltage, Zeiss, Germany. Microprobeanalysis was performed using DSM 940, Thungsten Kathod, Zeiss,Germany, Coupled EDX ISIS, SiLi-Detector, Energy resolution 133 eV,Oxford. Each analysis was preformed three times at different spotsusing screen analysis at very high magnication covering the wholesize of the spot.

Atomic Force Microscopy (AFM) images were taken using theDimension NanoScope IIIa Controller Scanning mode: tapping modeVeeco Instruments USA, to investigate the surface morphology on thecoated and uncoated substrate surfaces before corrosion.

Macroscopic images were taken using a digital optical metallo-graphic microscope VHX-100K, KEYENCE, Japan, to investigate thetypes of corrosion produced on the substrate surfaces after seven daysof immersion in 3.5% NaCl solution.

3. Results and discussion

3.1. Coatings characterization and surface examination

3.1.1. SEM-EDS micrographs and visual inspectionSEM micrograph of the uncoated aluminum samples before

immersion in 3.5% NaCl solution revealed presence of some surfacedefects which stimulate pitting corrosion on AA2024 alloys(Fig. 2a). After vanadia treatment, a relatively thick layer ofvanadium oxide depends on the vanadia concentration (about

40000

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50 g/l50 g/l

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vanadia concentration.Energy (keV)4 6

in 3.5% NaCl solution. The images focus into the healing behavior with increasing the

1.01.2 m) was formed. However, increasing the thickness due toincreasing the vanadia concentration affects negatively the coatingdistribution over aluminum substrate where many coating defectswere observed for the samples coated with 30 and 50 g/l vanadia(Figs. 3a, 4a and 5a).

After seven days of immersion in 3.5% NaCl solution, visualinspection and microscopic examination of the uncoated samplesshowed severe pitting as well as crevice corrosion (Fig. 6). The averagenumber of pits on the surface of the uncoated samples was 10 pits/cm2.A marked decrease in the crevice corrosion areas was observed for thevanadia coated samples (Figs. 3b, 4b and5b).Moreover, the number andthe size of pitting attack decreased sharply for the samples coated withvanadia. Thenumberof pitswas calculated to be less than2, 4 and8 pits/cm2 for the samples treated in 10, 30 and 50 g/l vanadia solutionrespectively (Fig. 6). The sample treated in 50 g/l solution showed adramatic decrease in the pitting and crevice corrosion resistance wheresevere corroded surface full of pits with a vanadia layer loosely adheredto the substrate. This indicates that increasing vanadia concentration(N10 g/l) adversely affected the coating efciency (Fig. 6). The chemicalreaction behind formation of loosely adhered coating in that case is notso clear and may be due to changing the vanadia-solution pH. The bestlocalized corrosion resistance was obtained from the samples thattreated with 10 g/l vanadia solution with a surface free of pitting andlimited zones of crevice (Figs. 3b, 4b 5b and Fig. 6).

3.1.2. Atomic Force Microscopy (AFM) examinationsThe surface topography and roughness of the aluminum

substrate before and after applying the vanadia coatings wereexamined by AFM. Uncoated aluminum substrates revealed a

naturally occurring aluminum oxide of high roughness distributedover the substrate (Fig. 7a). The phase image of uncoated substrateshowed aluminum oxide phase with some small areas of differentphases which can be explained by the different oxides formed dueto different alloying elements in the AA2024 alloy underinvestigation.

In general, vanadia coated samples (especially those treated atlower vanadia solution concentrations 10 and 30 g/l) revealed amore compact surface due to formation of vanadium rich oxidelms (Fig. 7b and c). Such lms are characterized by lowerroughness and hence, better and uniform surface distribution ofthe vanadia rich oxides over the Al substrate compared withuncoated and coated ones at higher (50 g/l) vanadia concentration(Fig. 7a, b, c and d). The phase images of vanadia coated substratesshowed two phases which can be explained by the formation ofvanadium-rich oxide incorporated in the aluminum oxide layer.

A comparison between images in Fig. 7b, c and d indicates thatincreasing the vanadia solution concentration from 10 g/l to 50 g/lincreases the surface roughness of the lm formed and hence,increase the chance for localized corrosion to occur. This observationcan be considered as another evidence for decreasing the corrosionresistance with increasing the vanadia concentration.

3.2. Electrochemical impedance spectroscopy

The corrosion resistance of AA2024 samples uncoated andcoated with vanadia solutions of different concentrations rangingfrom 0 to 50 g/l was investigated in 3.5% NaCl solution. According toNyquist plots (Fig. 8a), the surface resistance increases in presence

Uncoated 10 g/l

1673A.S. Hamdy et al. / Thin Solid Films 520 (2011) 1668167830 g/l

Crevice corrosion Pitting corrosion

Crevice corrosion Fig. 6. Macroscopic images for AA2024 samples treated in different vanadia conc50 g/l

Pitting corrosionCrevice corrosion entration solutions after seven days of free immersion in 3.5% NaCl solution.

1674 A.S. Hamdy et al. / Thin Solid Films 520 (2011) 16681678

Fig. 7. AFM of AA2024 substrate before corrosion. a. uncoated. b. 10 g/l vanadia coated c. 30 g/l vanadia coated d. 50 g/l vanadia coated.

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-1 0 1 2 3 4 5of vanadia coatings. However, increasing the concentration ofvanadia solution from 10 g/l up to 50 g/l seems to have an adverseeffect on the localized corrosion resistances. Generally, localizedcorrosion attack due to the presence of silicon as an alloyingelement in an aluminum matrix is the most common form ofcorrosion in AA2024 alloys. It is known that localized corrosion(pitting and crevice corrosion) is more dangerous than general(uniform) corrosion. Visual inspection (Fig. 6) revealed thatlocalized corrosion is the most predominant corrosion form in theuncoated samples. Conversely, the most predominant corrosionform in the vanadia coated samples is the general corrosionespecially for the samples coated with low vanadia concentration,i.e. 10 and 30 g/l (Fig. 6). The surface resistance measured by meanof electrochemical impedance spectroscopy is the summation oflocalized (pitting+crevice) and general corrosion resistances. Thiscan explain why the value of surface resistance seems to be higherin case of the uncoated samples (Fig. 8a) although severe localizedcorrosion occurred and the values measured for some vanadiacoated samples were relatively low although the localized corrosionattack decreased.

This result conrms the observation of SEM and visual inspectionwhere the number of pits was deceased to be less than 2 pits/cm2 forthe samples coated with 10 g/l vanadia solution (Fig. 6) which can beattributed to formation of a compact vanadium-rich oxide lmdistributed uniformly over the aluminum substrate (Fig. 7b).

The impedance spectra after one week of immersion in NaClsolution of bare AA2024 alloy and all vanadia treated samples showthe presence of two time constants (Fig. 8b). The time constant withthe maximum at around 1102 Hz in the phase angle plot attributedto the charge transfer resistance of corrosion process. However, thephase angle () of the sample coated with 10 g/l vanadia is 60 degree

log (frequency) [Hz]Fig. 8. a. Nyquist plots and b. Bode plots for uncoated and vanadia coated AA2024samples after seven days of immersion in 3.5% NaCl solution.and the other phase angles are 80 degree. The second additional timeconstant at low frequencies attributed to relaxation of mass transportin the solid phase due to the growth of the corrosion product layer.The time constant related to the corrosion process for all vanadiacoated samples (except 10 g/l vanadia) moves to higher frequencies,approaching to the bare Al substrate.

The presence of vanadia coating prepared in 10 g/l vanadiasolution promotes the increasing of the low frequency impedanceby almost 1.4 orders of magnitude compared to the bare Al alloy andother vanadia coating conditions. The reduction of impedance revealsthe deterioration of the protection system. The shift of phase angletowards zero at very low frequency (Fig. 8b) for the uncoated samplesand the samples coated with 30 g/l indicating the occurrence of thelocalized corrosion. Conversely, the samples coated with 10 g/lvanadia showed a stable phase angle at low frequency conrmingthe resistance to localized corrosion. The resistance and capacitancevalues associated with the vanadia-coating prepared in 10 g/l vanadiasolution reect good barrier properties, associated with the imped-iment of the electrolyte to reach the metallic substrate.

Based on EIS results and microscopic examination, the treatmentof AA2024 with vanadia at low concentration (10 g/l) improves theresistance to localized corrosion due to the formation of the protectivevanadia rich oxide lm which acts as a barrier to prevent the oxygendiffusion to the metal surface and therefore, impede corrosion but notprevent it as conrmed by microscopic examination. Because the lmformed is relatively thin about 1 to 1.5 m (Fig. 9), general corrosion(but not the dangerous localized corrosion) increased due to diffusionof chloride ions through these lms (Figs. 26). Moreover, treatmentwith 10 g/l vanadia solution plays an important role in inhibiting theactive surface sites by blocking and repairing the micro-cracks andpits (Figs. 25).

3.3. Cyclic voltammetry

Cyclic voltammetry (Fig. 10) was used to evaluate the pittingcorrosion resistance of the AA2024 samples treated with vanadia afterimmersion in 3.5% NaCl solution. Generally, the results of cyclicvoltammetry of the vanadia treated samples conrmed the previousresults of EIS and microscopic examination. The samples coated with10 g/l vanadia solution showed the smallest loop area which meansthat such treatment offered the best resistance to pitting corrosion. Onthe other hand, the other vanadia treated samples showed alsoacceptable localized corrosion resistances compared with theuncoated samples but still less than the resistance obtained from10 g/l vanadia solution. This can be explained by the fact that thesurface resistance obtained from EIS data is the summation of pittingand general corrosion resistance and conrms why the samplestreated with 10 g/l vanadia solution showed a marked corrosionresistance compared with the other pretreatment conditions.

4. Conclusion

1. Surface treatment of AA2024with vanadia at low concentration is apromising method for improving localized corrosion resistance.

2. Based on the surface examination, EIS and polarization measure-ments, treatment of Al substrate with 10 g/l vanadia solution playsan important role in inhibiting the active surface sites by blockingand repairing the pits.

3. Improving the localized corrosion resistance through a simpletechnique that based on surface treatment in a very diluted vanadiasolution seems to have a very promising industrial approach inmany strategic applications such as automotive and aerospaceindustries taking into account that these vanadia coatingswould beonly a pre-treatment trying to provide a self-healing functionality,and a nal top coat will be crucial to reach an adequate corrosion

protection.

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This project was funded through an Alexander von HumboldtResearch Award for Experienced Researchers granted to Dr. AbdelSalam Hamdy. The authors would like to thank Dr. Hartmann, MaxPlanck Institute of Colloids and Interfaces, Germany, for his guidancewith the SEM-EDS surface examination.

Fig. 10. Cyclic voltammetry curves after seven days of immersion in 3.5% NaCl solution.

00

Fig. 9. Cross-cut for the vanadia coated (10 g/l) samples before (a) and after (b) one week ointo the coating thickness ~1 m and how corrosion attack looks like from a side view.Energy (keV)2 4 6The authors would also like to thank Center of Research Excellencein Corrosion, King Fahd University of Petroleum & Minerals, Dhahran31261, Saudi Arabia, for funding the participation of Dr. Abdel SalamHamdy in the 38th International Conference onMetallurgical Coatingsand Thin Films, May 2010, San Diego, CA, USA.

References

[1] R.L. Twite, G.P. Bierwagen, Prog. Org. Coat. 33 (1998) 91.[2] A.S. Hamdy, D.P. Butt, J. Surf. Coat. Technol. Vol. 201/1-2 (2006) 401.[3] A.S. Hamdy, Prog. Org. Coat 56 (2006) 146.[4] S.S. Pathak, A.S. Khanna, Prog. Org. Coat. 65 (2009) 288.[5] A.S. Hamdy, J. Materials, Letters 60 (2006) 2633.[6] A.S. Hamdy, M. Shoeib, D. Butt, A novel approach in designing environmentally

compliant sol-gel based ceramic coatings and nanocomposite coatings forindustrial applications, in: A. Malik, R.J. Rawat (Eds.), New Nanotechniques,Nova Science Publishers, New York, USA, ISBN: 978-1-60692-516-4, 2009, p. 649,Chapter 20.

[7] A.S. Hamdy, Prog. Org. Coat. 55 (2006) 218.[8] A. Simoes, D. Battocchi, D. Tallman, G. Bierwagen, Prog. Org. Coat. 63 (2008) 260.[9] S. Pathak, M. Blanton, S. Mendon, J. Rawlins, Corros. Sci. 52 (2010) 3782.

[10] A.S. Hamdy (Editor): High Performance Coatings for Automotive and AerospaceIndustries, Nova Science Publishers, NY, USA, ISBN: 978-1-60876-579-9.

[11] A.S. Hamdy, A.M. Beccaria, J. Appl. Electrochem. 35 (2005) 473.[12] A.S. Hamdy, A.M. Beccaria, P. Traverso, J. Appl. Electrochem. 35 (2005) 467.[13] A.S. Hamdy, A.M. Beccaria, R. Spiniello, Corros. Prev. Control Vol. 48 (No. 3) (2001)

101.[14] A.S. Hamdy, A.M. Beccaria, Surf. Interface Anal. Vol. 34 (2002) 160.[15] A.S. Hamdy, A.M. Beccaria, Surf. Interface Anal. Vol. 34 (2002) 171.[16] A.S. Hamdy, J. Surf. Coat Technol. Vol. 200 (No. 1213) (2006) 3786.[17] A.S. Hamdy, A.M. Beccaria, Corros. Prev. Control Vol. 48 (No. 4) (2001) 143.[18] A.S. Hamdy, A.M. Beccaria, T. Temtchenko, Surf. Coat. Tech. Vol. 155 (2002) 184.[19] A.S. Hamdy, B. Marx, D. Butt, Mater. Chem. Phys. 127 (2011) 253.[20] H. Schfer, H.-R. Stock, Corros. Sci. 47 (4) (2005) 953.[21] G. Selvaduray, L. Sheet, Mater. Sci. Tech. Vol. 9 (1993) 463.

Energy (keV)2 4 6

f corrosion in 3.5% NaCl solution and the corresponding EDS analysis. The images focus

[22] J. Haussonne, J. Lostec, S. Sadou, Am. Ceram. Soc. Bull. Vol. 72 (5) (1993) 84.[23] J. Lee, I. Lee, D. Kim, Y. Ahn, H. Chung, J. Mater. Sci. Forum Vols. 449452 (2004)

213.[24] Y.Z. Shen, K.H. Oh, D.N. Lee, Scr. Mater. 53 (2005) 1345.[25] T. Okada, M. Toriyama, S. Kanzaki, J. Mater. Sci. 35 (2000) 3105.

[26] A.S. Hamdy, D.P. Butt, J. Anti-Corros. Meth. Mater. Vol. 53 (4) (2006) 240.[27] A.S. Hamdy, D.P. Butt, J. Mater. Process. Technol. Vol. 181 (No. 13) (2007) 76.[28] A.S. Hamdy, D.P. Butt, A.A. Ismail, J. Electrochim. Acta 52 (2007) 3310.[29] A.S. Hamdy, I. Doench, H. Mhwald, J. Electrochim. Acta 56 (2011) 2493.

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Intelligent self-healing corrosion resistant vanadia coating for AA20241. Introduction2. Experimental2.1. Materials and surface preparation2.2. Solutions and surface treatment2.3. Testing2.3.1. Electrochemical impedance spectroscopy (EIS)2.3.2. Cyclic voltammetry measurements2.3.3. Surface characterization

3. Results and discussion3.1. Coatings characterization and surface examination3.1.1. SEM-EDS micrographs and visual inspection3.1.2. Atomic Force Microscopy (AFM) examinations

3.2. Electrochemical impedance spectroscopy3.3. Cyclic voltammetry

4. ConclusionAcknowledgmentsReferences